This is kind of a presumptuous question coming from someone who gets seriously stressed when it comes to "baking" and isn't very good at it at all ... but couldn't you simply use poppy seed cake batter in muffin tins / cupcake thingys and adjust the baking time a bit?

Zereh, I would consider your version a poppyseed cupcake. I home bake a lot, but don't have as much experience (commercial and home baking) as many on this forum. Personally I would think that a muffin is more dense than a cupcake or cake. Though some muffins are "lighter", I still think they are different from cake.

example: I tried making a banana cake. I wanted to recreate something I used to be able to buy and can no longer get. I took a banana bread recipe and used that as cake (with one slight modification) and it definitely was still banana bread. I eventually found a banana cake recipe that's really good. I have yet to sit down and compare the two recipes but definitely will soon.